Method for radio resource measurement in wireless access system supporting carrier aggregation, and apparatus supporting same

ABSTRACT

The present invention relates to methods for making radio resource measurements in synchronized cells when quasi co-location is applied, and to apparatuses supporting same. A method for a terminal for making radio resource measurements (RRM) in a wireless access system according to one embodiment of the present invention may comprise the steps of: receiving an upper level signal comprising a reference signal for channel state information (CSI-RS) of a first cell, and quasi co-location (QCL) information for a cell-specific reference signal (CRS) and/or CSI-RS of a second cell; receiving the CRS and/or CSI-RS of the second cell on the basis of the QCL information; and measuring a first RRM for the first cell by means of the CRS and/or the CSI-RS of the second cell.

TECHNICAL FIELD

The present invention relates to a wireless access system and, moreparticularly, to methods for performing Radio Resource Measurement (RRM)in a synchronized cell when Quasi Co-Location (QCL) is applied andapparatuses supporting the same.

BACKGROUND ART

Wireless access systems have been widely deployed to provide varioustypes of communication services such as voice or data. In general, awireless access system is a multiple access system that supportscommunication of multiple users by sharing available system resources (abandwidth, transmission power, etc.) among them. For example, multipleaccess systems include a Code Division Multiple Access (CDMA) system, aFrequency Division Multiple Access (FDMA) system, a Time DivisionMultiple Access (TDMA) system, an Orthogonal Frequency Division MultipleAccess (OFDMA) system, and a Single Carrier Frequency Division MultipleAccess (SC-FDMA) system.

DISCLOSURE Technical Problem

An object of the present invention is to provide an efficient datatransmission method in a carrier aggregation environment.

Another object of the present invention is to provide methods forperforming RRM in a synchronized cell to which QCL is applied.

Another object of the present invention is to provide a method forsetting cyclic prefix lengths of a synchronized cell and anon-synchronized cell when QCL is applied.

Another object of the present invention is to provide a method forallocating cell identifiers of a synchronized cell and anon-synchronized cell when QCL is applied.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present disclosure are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present disclosure could achieve will be more clearlyunderstood from the following detailed description.

Technical Solution

The present invention provides methods for performing RRM in asynchronized cell when QCL is applied and apparatuses supporting thesame.

In an aspect of the present invention, a method for performing RadioResource Measurement (RRM) by a User Equipment (UE) in a radio accesssystem is provided. The method may include receiving a higher layersignal including information about Quasi Co-Location (QCL) between aChannel State Information Reference Signal (CSI-RS) of a first cell anda Cell-specific Reference Signal (CRS) and/or a CSI-RS of a second cell,receiving the CRS and/or the CSI-RS of the second cell based on theinformation about QCL, and performing first RRM for the first cell usingthe CRS and/or the CSI-RS of the second cell.

Synchronization for the first cell may be maintained using asynchronization signal transmitted in the second cell.

The method may further include performing second RRM for the first cellusing the CSI-RS of the first cell.

The first RRM may include one or more of Reference Signal Received Power(RSRP) measurement and Path Loss (PL) measurement, and the second RRMmay include one or more of Reference Signal Received Quality (RSRQ) andPL measurement.

The first cell may be a synchronized cell in which a synchronizationsignal is not transmitted, the second cell may be a synchronizationreference cell in which the synchronization signal is transmitted, andthe UE may not receive a downlink signal from the first cell while theUE receives the CRS and/or the CSI-RS of the second cell from the secondcell.

The first cell may be a New Carrier Type (NCT) to which one or more of asynchronization signal, a CRS, a downlink broadcast channel, and adownlink control channel are not allocated, and the second cell may be alegacy serving cell.

In another aspect of the present invention, a User Equipment (UE) forperforming Radio Resource Measurement (RRM) in a radio access system isprovided. The UE may include a transmission module, a reception module,and a processor supporting RRM.

The processor may be configured to receive a higher layer signalincluding information about Quasi Co-Location (QCL) between a ChannelState Information Reference Signal (CSI-RS) of a first cell and aCell-specific Reference Signal (CRS) and/or a CSI-RS of a second cellthrough the reception module, receive the CRS and/or the CSI-RS of thesecond cell based on the information about QCL through the receptionmodule, and perform first RRM for the first cell using the CRS and/orthe CSI-RS of the second cell.

Synchronization for the first cell may be maintained using asynchronization signal transmitted in the second cell.

The processor may be configured to further perform second RRM for thefirst cell using the CSI-RS of the first cell.

The first RRM may include one or more of Reference Signal Received Power(RSRP) measurement and Path Loss (PL) measurement, and the second RRMmay include one or more of Reference Signal Received Quality (RSRQ) andPL measurement.

The first cell may be a synchronized cell in which a synchronizationsignal is not transmitted, the second cell may be a synchronizationreference cell in which the synchronization signal is transmitted, andthe UE may not receive a downlink signal from the first cell while theUE receives the CRS and/or the CSI-RS of the second cell from the secondcell.

The first cell may be a New Carrier Type (NCT) to which one or more of asynchronization signal, a CRS, a downlink broadcast channel, and adownlink control channel are not allocated, and the second cell may be alegacy serving cell.

The afore-described aspects of the present disclosure are merely a partof embodiments of the present disclosure. Those skilled in the art willderive and understand various embodiments reflecting the technicalfeatures of the present disclosure from the following detaileddescription of the present disclosure.

Advantageous Effects

According to the embodiments of the present disclosure, the followingeffects can be achieved.

First, downlink data can be efficiently transmitted and received in acarrier aggregation environment.

Second, RRM can be performed in a synchronized cell to which QCL isapplied.

Third, timing synchronization can be accurately obtained and maintainedby setting a cyclic prefix length between a synchronized cell and anon-synchronized cell when QCL is applied.

Fourth, a cell identifier shortage problem can be solved by setting acell identifier of a synchronized cell according to a non-synchronizedcell when QCL is applied.

It will be appreciated by persons skilled in the art that that theeffects that can be achieved through the present disclosure are notlimited to what has been particularly described hereinabove and otheradvantages of the present disclosure will be more clearly understoodfrom the following detailed description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 illustrates physical channels and a general signal transmissionmethod using the physical channels;

FIG. 2 illustrates radio frame structures;

FIG. 3 illustrates a structure of a DownLink (DL) resource grid for theduration of one DL slot;

FIG. 4 illustrates a structure of an UpLink (UL) subframe;

FIG. 5 illustrates a structure of a DL subframe;

FIG. 6 illustrates a cross carrier-scheduled subframe structure in theLTE-A system;

FIG. 7 illustrates a subframe to which cell specific reference signals(CRSs) are allocated;

FIG. 8 illustrates an example of subframes to which channel stateinformation reference signals (CSI-RSs) are allocated according to thenumber of antenna ports;

FIG. 9 illustrates an example of a subframe to which UE-specificReference Signals (UE-RSs) are allocated;

FIG. 10 illustrates an example of a frame structure in whichsynchronization signal transmission positions are indicated;

FIG. 11 illustrates a secondary synchronization signal generationmethod;

FIG. 12 illustrates an example of a Radio Resource Measurement (RRM)method;

FIG. 13 illustrates another example of an RRM method;

FIG. 14 illustrates another example of an RRM method;

FIG. 15 illustrates an example of a UE-RS pattern in a serving cell towhich a normal Cyclic Prefix (CP) is applied in FDD; and

FIG. 16 illustrates means that can implement the methods described withreference to FIGS. 1 to 11.

BEST MODE

The present invention provides methods for performing Radio ResourceMeasurement (RRM) in a synchronized cell when Quasi Co-Location (QCL) isapplied and apparatuses performing the same.

The embodiments of the present disclosure described below arecombinations of elements and features of the present disclosure inspecific forms. The elements or features may be considered selectiveunless otherwise mentioned. Each element or feature may be practicedwithout being combined with other elements or features. Further, anembodiment of the present disclosure may be constructed by combiningparts of the elements and/or features. Operation orders described inembodiments of the present disclosure may be rearranged. Someconstructions or elements of any one embodiment may be included inanother embodiment and may be replaced with corresponding constructionsor features of another embodiment.

In the description of the attached drawings, a detailed description ofknown procedures or steps of the present disclosure will be avoided lestit should obscure the subject matter of the present disclosure. Inaddition, procedures or steps that could be understood to those skilledin the art will not be described either.

In the embodiments of the present disclosure, a description is mainlymade of a data transmission and reception relationship between a BaseStation (BS) and a User Equipment (UE). A BS refers to a terminal nodeof a network, which directly communicates with a UE. A specificoperation described as being performed by the BS may be performed by anupper node of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with a UE may be performed by the BS, or network nodesother than the BS. The term ‘BS’ may be replaced with a fixed station, aNode B, an evolved Node B (eNode B or eNB), an Advanced Base Station(ABS), an access point, etc.

In the embodiments of the present disclosure, the term terminal may bereplaced with a UE, a Mobile Station (MS), a Subscriber Station (SS), aMobile Subscriber Station (MSS), a mobile terminal, an Advanced MobileStation (AMS), etc.

A transmitter is a fixed and/or mobile node that provides a data serviceor a voice service and a receiver is a fixed and/or mobile node thatreceives a data service or a voice service. Therefore, a UE may serve asa transmitter and a BS may serve as a receiver, on an UpLink (UL).Likewise, the UE may serve as a receiver and the BS may serve as atransmitter, on a DownLink (DL).

The embodiments of the present disclosure may be supported by standardspecifications disclosed for at least one of wireless access systemsincluding an Institute of Electrical and Electronics Engineers (IEEE)802.xx system, a 3rd Generation Partnership Project (3GPP) system, a3GPP Long Term Evolution (LTE) system, and a 3GPP2 system. Inparticular, the embodiments of the present disclosure may be supportedby the standard specifications, 3GPP TS 36.211, 3GPP TS 36.212, 3GPP TS36.213, and 3GPP TS 36.321. That is, the steps or parts, which are notdescribed to clearly reveal the technical idea of the presentdisclosure, in the embodiments of the present disclosure may beexplained by the above standard specifications. All terms used in theembodiments of the present disclosure may be explained by the standardspecifications.

Reference will now be made in detail to the embodiments of the presentdisclosure with reference to the accompanying drawings. The detaileddescription, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present disclosure, rather than to show the only embodiments thatcan be implemented according to the invention.

The following detailed description includes specific terms in order toprovide a thorough understanding of the present disclosure. However, itwill be apparent to those skilled in the art that the specific terms maybe replaced with other terms without departing the technical spirit andscope of the present disclosure. In addition, all of the terms disclosedby the present description can be explained based on the standardspecification documents.

The embodiments of the present disclosure can be applied to variouswireless access systems such as Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), SingleCarrier Frequency Division Multiple Access (SC-FDMA), etc.

CDMA may be implemented as a radio technology such as UniversalTerrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented asa radio technology such as Global System for Mobile communications(GSM)/General packet Radio Service (GPRS)/Enhanced Data Rates for GSMEvolution (EDGE). OFDMA may be implemented as a radio technology such asIEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Evolved UTRA(E-UTRA), etc.

UTRA is a part of Universal Mobile Telecommunications System (UMTS).3GPP LTE is a part of Evolved UMTS (E-UMTS) using E-UTRA, adopting OFDMAfor DL and SC-FDMA for UL. LTE-Advanced (LTE-A) is an evolution of 3GPPLTE. While the embodiments of the present disclosure are described inthe context of a 3GPP LTE/LTE-A system in order to clarify the technicalfeatures of the present disclosure, the present disclosure is alsoapplicable to an IEEE 802.16e/m system, etc.

1. 3GPP LTE/LTE-A System

In a wireless access system, a UE receives information from an eNB on aDL and transmits information to the eNB on a UL. The informationtransmitted and received between the UE and the eNB includes generaldata information and various types of control information. There aremany physical channels according to the types/usages of informationtransmitted and received between the eNB and the UE.

1.1 System Overview

FIG. 1 illustrates physical channels and a general method using thephysical channels, which may be used in embodiments of the presentdisclosure.

When a UE is powered on or enters a new cell, the UE performs initialcell search (S11). The initial cell search involves acquisition ofsynchronization to an eNB. Specifically, the UE synchronizes its timingto the eNB and acquires information such as a cell Identifier (ID) byreceiving a Primary Synchronization Channel (P-SCH) and a SecondarySynchronization Channel (S-SCH) from the eNB.

Then the UE may acquire information broadcast in the cell by receiving aPhysical Broadcast Channel (PBCH) from the eNB. During the initial cellsearch, the UE may monitor a DL channel state by receiving a DownlinkReference Signal (DL RS).

After the initial cell search, the UE may acquire more detailed systeminformation by receiving a Physical Downlink Control Channel (PDCCH) andreceiving a Physical Downlink Shared Channel (PDSCH) based oninformation of the PDCCH (S12).

To complete connection to the eNB, the UE may perform a random accessprocedure with the eNB (S13 to S16). In the random access procedure, theUE may transmit a preamble on a Physical Random Access Channel (PRACH)(S13) and may receive a PDCCH and a PDSCH associated with the PDCCH(S14). In the case of contention-based random access, the UE mayadditionally perform a contention resolution procedure includingtransmission of an additional PRACH (S15) and reception of a PDCCHsignal and a PDSCH signal corresponding to the PDCCH signal (S16).

After the above procedure, the UE may receive a PDCCH and/or a PDSCHfrom the eNB (S17) and transmit a Physical Uplink Shared Channel (PUSCH)and/or a Physical Uplink Control Channel (PUCCH) to the eNB (S18), in ageneral UL/DL signal transmission procedure.

Control information that the UE transmits to the eNB is genericallycalled Uplink Control Information (UCI). The UCI includes a HybridAutomatic Repeat and reQuest Acknowledgement/Negative Acknowledgement(HARQ-ACK/NACK), a Scheduling Request (SR), a Channel Quality Indicator(CQI), a Precoding Matrix Index (PMI), a Rank Indicator (RI), etc.

In the LTE system, UCI is generally transmitted on a PUCCH periodically.However, if control information and traffic data should be transmittedsimultaneously, the control information and traffic data may betransmitted on a PUSCH. In addition, the UCI may be transmittedaperiodically on the PUSCH, upon receipt of a request/command from anetwork.

FIG. 2 illustrates exemplary radio frame structures used in embodimentsof the present disclosure.

FIG. 2( a) illustrates frame structure type 1. Frame structure type 1 isapplicable to both a full Frequency Division Duplex (FDD) system and ahalf FDD system.

One radio frame is 10 ms (T_(f)=307200·T_(s)) long, includingequal-sized 20 slots indexed from 0 to 19. Each slot is 0.5 ms(T_(slot)=15360·T_(s)) long. One subframe includes two successive slots.An i^(th) subframe includes 2i^(th) and (2i+1)^(th) slots. That is, aradio frame includes 10 subframes. A time required for transmitting onesubframe is defined as a Transmission Time Interval (TTI). T_(s) is asampling time given as T_(s)=1/(15 kHz×2048)=3.2552×10⁻⁸ (about 33 ns).One slot includes a plurality of Orthogonal Frequency DivisionMultiplexing (OFDM) symbols or SC-FDMA symbols in the time domain by aplurality of Resource Blocks (RBs) in the frequency domain.

A slot includes a plurality of OFDM symbols in the time domain. SinceOFDMA is adopted for DL in the 3GPP LTE system, one OFDM symbolrepresents one symbol period. An OFDM symbol may be called an SC-FDMAsymbol or symbol period. An RB is a resource allocation unit including aplurality of contiguous subcarriers in one slot.

In a full FDD system, each of 10 subframes may be used simultaneouslyfor DL transmission and UL transmission during a 10-ms duration. The DLtransmission and the UL transmission are distinguished by frequency. Onthe other hand, a UE cannot perform transmission and receptionsimultaneously in a half FDD system.

The above radio frame structure is purely exemplary. Thus, the number ofsubframes in a radio frame, the number of slots in a subframe, and thenumber of OFDM symbols in a slot may be changed.

FIG. 2( b) illustrates frame structure type 2. Frame structure type 2 isapplied to a Time Division Duplex (TDD) system. One radio frame is 10 ms(T_(f)=307200·T_(s)) long, including two half-frames each having alength of 5 ms (=153600·T_(s)) long. Each half-frame includes fivesubframes each being 1 ms (=30720·T_(s)) long. An i^(th) subframeincludes 2i^(th) and (2i+1)^(th) slots each having a length of 0.5 ms(T_(slot)=15360·T_(s)). T_(s) is a sampling time given as T_(s)=1/(15kHz×2048)=3.2552×10⁻⁸ (about 33 ns).

A type-2 frame includes a special subframe having three fields, DownlinkPilot Time Slot (DwPTS), Guard Period (GP), and Uplink Pilot Time Slot(UpPTS). The DwPTS is used for initial cell search, synchronization, orchannel estimation at a UE, and the UpPTS is used for channel estimationand UL transmission synchronization with a UE at an eNB. The GP is usedto cancel UL interference between a UL and a DL, caused by themulti-path delay of a DL signal.

[Table 1] below lists special subframe configurations (DwPTS/GP/UpPTSlengths).

TABLE 1 Normal cyclic prefix in downlink Extended cyclic prefix indownlink UpPTS UpPTS Special Normal Extended Normal Extended subframecyclic prefix cyclic prefix cyclic prefix cyclic prefix configurationDwPTS in uplink in uplink DwPTS in uplink in uplink 0  6592 · T_(s) 2192· T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 1 19760 ·T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 · T_(s) 25600· T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 · T_(s) 5  6592· T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 · T_(s) 23040 ·T_(s) 7 21952 · T_(s) — — — 8 24144 · T_(s) — — —

FIG. 3 illustrates an exemplary structure of a DL resource grid for theduration of one DL slot, which may be used in embodiments of the presentdisclosure.

Referring to FIG. 3, a DL slot includes a plurality of OFDM symbols inthe time domain. One DL slot includes 7 OFDM symbols in the time domainand an RB includes 12 subcarriers in the frequency domain, to which thepresent disclosure is not limited.

Each element of the resource grid is referred to as a Resource Element(RE). An RB includes 12×7 REs. The number of RBs in a DL slot, NDLdepends on a DL transmission bandwidth. A UL slot may have the samestructure as a DL slot.

FIG. 4 illustrates a structure of a UL subframe which may be used inembodiments of the present disclosure.

Referring to FIG. 4, a UL subframe may be divided into a control regionand a data region in the frequency domain. A PUCCH carrying UCI isallocated to the control region and a PUSCH carrying user data isallocated to the data region. To maintain a single carrier property, aUE does not transmit a PUCCH and a PUSCH simultaneously. A pair of RBsin a subframe are allocated to a PUCCH for a UE. The RBs of the RB pairoccupy different subcarriers in two slots. Thus it is said that the RBpair frequency-hops over a slot boundary.

FIG. 5 illustrates a structure of a DL subframe that may be used inembodiments of the present disclosure.

Referring to FIG. 5, up to three OFDM symbols of a DL subframe, startingfrom OFDM symbol 0 are used as a control region to which controlchannels are allocated and the other OFDM symbols of the DL subframe areused as a data region to which a PDSCH is allocated. DL control channelsdefined for the 3GPP LTE system include a Physical Control FormatIndicator Channel (PCFICH), a PDCCH, and a Physical Hybrid ARQ IndicatorChannel (PHICH).

The PCFICH is transmitted in the first OFDM symbol of a subframe,carrying information about the number of OFDM symbols used fortransmission of control channels (i.e. the size of the control region)in the subframe. The PHICH is a response channel to a UL transmission,delivering an HARQ ACK/NACK signal. Control information carried on thePDCCH is called Downlink Control Information (DCI). The DCI transportsUL resource assignment information, DL resource assignment information,or UL Transmission (Tx) power control commands for a UE group.

1.2 Carrier Aggregation (CA) Environment

1.2.1 CA Overview

A 3GPP LTE system (conforming to Rel-8 or Rel-9) (hereinafter, referredto as an LTE system) uses Multi-Carrier Modulation (MCM) in which asingle Component Carrier (CC) is divided into a plurality of bands. Incontrast, a 3GPP LTE-A system (hereinafter, referred to an LTE-A system)may use CA by aggregating one or more CCs to support a broader systembandwidth than the LTE system. The term CA is interchangeably used withcarrier combining, multi-CC environment, or multi-carrier environment.

In the present invention, multi-carrier means CA (or carrier combining).Herein, CA covers aggregation of contiguous carriers and aggregation ofnon-contiguous carriers. The number of aggregated CCs may be differentfor a DL and a UL. If the number of DL CCs is equal to the number of ULCCs, this is called symmetric aggregation. If the number of DL CCs isdifferent from the number of UL CCs, this is called asymmetricaggregation. The term CA is interchangeable with carrier combining,bandwidth aggregation, spectrum aggregation, etc.

The LTE-A system aims to support a bandwidth of up to 100 MHz byaggregating two or more CCs, that is, by CA. To guarantee backwardcompatibility with a legacy IMT system, each of one or more carriers,which has a smaller bandwidth than a target bandwidth, may be limited toa bandwidth used in the legacy system.

For example, the legacy 3GPP LTE system supports bandwidths {1.4, 3, 5,10, 15, and 20 MHz} and the 3GPP LTE-A system may support a broaderbandwidth than 20 MHz using these LTE bandwidths. A CA system of thepresent invention may support CA by defining a new bandwidthirrespective of the bandwidths used in the legacy system.

There are two types of CA, intra-band CA and inter-band CA. Intra-bandCA means that a plurality of DL CCs and/or UL CCs are successive oradjacent in frequency. In other words, the carrier frequencies of the DLCCs and/or UL CCs are positioned in the same band. On the other hand, anenvironment where CCs are far away from each other in frequency may becalled inter-band CA. In other words, the carrier frequencies of aplurality of DL CCs and/or UL CCs are positioned in different bands. Inthis case, a UE may use a plurality of Radio Frequency (RF) ends toconduct communication in a CA environment.

The LTE-A system adopts the concept of cell to manage radio resources.The above-described CA environment may be referred to as a multi-cellenvironment. A cell is defined as a pair of DL and UL CCs, although theUL resources are not mandatory. Accordingly, a cell may be configuredwith DL resources alone or DL and UL resources.

For example, if one serving cell is configured for a specific UE, the UEmay have one DL CC and one UL CC. If two or more serving cells areconfigured for the UE, the UE may have as many DL CCs as the number ofthe serving cells and as many UL CCs as or fewer UL CCs than the numberof the serving cells, or vice versa. That is, if a plurality of servingcells are configured for the UE, a CA environment using more UL CCs thanDL CCs may also be supported.

CA may be regarded as aggregation of two or more cells having differentcarrier frequencies (center frequencies). Herein, the term ‘cell’ shouldbe distinguished from ‘cell’ as a geographical area covered by an eNB.Hereinafter, intra-band CA is referred to as intra-band multi-cell andinter-band CA is referred to as inter-band multi-cell.

In the LTE-A system, a Primacy Cell (PCell) and a Secondary Cell (SCell)are defined. A PCell and an SCell may be used as serving cells. For a UEin RRC_CONNECTED state, if CA is not configured for the UE or the UEdoes not support CA, a single serving cell including only a PCell existsfor the UE. On the contrary, if the UE is in RRC_CONNECTED state and CAis configured for the UE, one or more serving cells may exist for theUE, including a PCell and one or more SCells.

Serving cells (PCell and SCell) may be configured by an RRC parameter. Aphysical-layer ID of a cell, PhysCellId is an integer value ranging from0 to 503. A short ID of an SCell, SCellIndex is an integer value rangingfrom 1 to 7. A short ID of a serving cell (PCell or SCell),ServeCellIndex is an integer value ranging from 1 to 7. IfServeCellIndex is 0, this indicates a PCell and the values ofServeCellIndex for SCells are pre-assigned. That is, the smallest cellID (or cell index) of ServeCellIndex indicates a PCell.

A PCell refers to a cell operating in a primary frequency (or a primaryCC). A UE may use a PCell for initial connection establishment orconnection reestablishment. The PCell may be a cell indicated duringhandover. In addition, the PCell is a cell responsible forcontrol-related communication among serving cells configured in a CAenvironment. That is, PUCCH allocation and transmission for the UE maytake place only in the PCell. In addition, the UE may use only the PCellin acquiring system information or changing a monitoring procedure. AnEvolved Universal Terrestrial Radio Access Network (E-UTRAN) may changeonly a PCell for a handover procedure by a higher-layerRRCConnectionReconfiguraiton message including mobilityControlInfo to aUE supporting CA.

An SCell may refer to a cell operating in a secondary frequency (or asecondary CC). Although only one PCell is allocated to a specific UE,one or more SCells may be allocated to the UE. An SCell may beconfigured after RRC connection establishment and may be used to provideadditional radio resources. There is no PUCCH in cells other than aPCell, that is, in SCells among serving cells configured in the CAenvironment.

When the E-UTRAN adds an SCell to a UE supporting CA, the E-UTRAN maytransmit all system information related to operations of related cellsin RRC_CONNECTED state to the UE by dedicated signaling. Changing systeminformation may be controlled by releasing and adding a related SCell.Herein, a higher-layer RRCConnectionReconfiguration message may be used.The E-UTRAN may transmit a dedicated signal having a different parameterfor each cell rather than it broadcasts in a related SCell.

After an initial security activation procedure starts, the E-UTRAN mayconfigure a network including one or more SCells by adding the SCells toa PCell initially configured during a connection establishmentprocedure. In the CA environment, each of a PCell and an SCell mayoperate as a CC. Hereinbelow, a Primary CC (PCC) and a PCell may be usedin the same meaning and a Secondary CC (SCC) and an SCell may be used inthe same meaning in embodiments of the present invention.

1.2.2 Cross Carrier Scheduling

Two scheduling schemes, self-scheduling and cross carrier scheduling aredefined for a CA system, from the perspective of carriers or servingcells. Cross carrier scheduling may be called cross CC scheduling orcross cell scheduling.

In self-scheduling, a PDCCH (carrying a DL grant) and a PDSCH aretransmitted in the same DL CC or a PUSCH is transmitted in a UL CClinked to a DL CC in which a PDCCH (carrying a UL grant) is received.

In cross carrier scheduling, a PDCCH (carrying a DL grant) and a PDSCHare transmitted in different DL CCs or a PUSCH is transmitted in a UL CCother than a UL CC linked to a DL CC in which a PDCCH (carrying a ULgrant) is received.

Cross carrier scheduling may be activated or deactivated UE-specificallyand indicated to each UE semi-statically by higher-layer signaling (e.g.RRC signaling).

If cross carrier scheduling is activated, a Carrier Indicator Field(CIF) is required in a PDCCH to indicate a DL/UL CC in which aPDSCH/PUSCH indicated by the PDCCH is to be transmitted. For example,the PDCCH may allocate PDSCH resources or PUSCH resources to one of aplurality of CCs by the CIF. That is, when a PDCCH of a DL CC allocatesPDSCH or PUSCH resources to one of aggregated DL/UL CCs, a CIF is set inthe PDCCH. In this case, the DCI formats of LTE Release-8 may beextended according to the CIF. The CIF may be fixed to three bits andthe position of the CIF may be fixed irrespective of a DCI format size.In addition, the LTE Release-8 PDCCH structure (the same coding andresource mapping based on the same CCEs) may be reused.

On the other hand, if a PDCCH transmitted in a DL CC allocates PDSCHresources of the same DL CC or allocates PUSCH resources in a single ULCC linked to the DL CC, a CIF is not set in the PDCCH. In this case, theLTE Release-8 PDCCH structure (the same coding and resource mappingbased on the same CCEs) may be used.

If cross carrier scheduling is available, a UE needs to monitor aplurality of PDCCHs for DCI in the control region of a monitoring CCaccording to the transmission mode and/or bandwidth of each CC.Accordingly, an appropriate SS configuration and PDCCH monitoring areneeded for the purpose.

In the CA system, a UE DL CC set is a set of DL CCs scheduled for a UEto receive a PDSCH, and a UE UL CC set is a set of UL CCs scheduled fora UE to transmit a PUSCH. A PDCCH monitoring set is a set of one or moreDL CCs in which a PDCCH is monitored. The PDCCH monitoring set may beidentical to the UE DL CC set or may be a subset of the UE DL CC set.The PDCCH monitoring set may include at least one of the DL CCs of theUE DL CC set. Or the PDCCH monitoring set may be defined irrespective ofthe UE DL CC set. DL CCs included in the PDCCH monitoring set may beconfigured to always enable self-scheduling for UL CCs linked to the DLCCs. The UE DL CC set, the UE UL CC set, and the PDCCH monitoring setmay be configured UE-specifically, UE group-specifically, orcell-specifically.

If cross carrier scheduling is deactivated, this implies that the PDCCHmonitoring set is always identical to the UE DL CC set. In this case,there is no need for signaling the PDCCH monitoring set. However, ifcross carrier scheduling is activated, the PDCCH monitoring set ispreferably defined within the UE DL CC set. That is, the eNB transmits aPDCCH only in the PDCCH monitoring set to schedule a PDSCH or PUSCH forthe UE.

FIG. 6 illustrates a cross carrier-scheduled subframe structure in theLTE-A system, which is used in embodiments of the present invention.

Referring to FIG. 6, three DL CCs are aggregated for a DL subframe forLTE-A UEs. DL CC ‘A’ is configured as a PDCCH monitoring DL CC. If a CIFis not used, each DL CC may deliver a PDCCH that schedules a PDSCH inthe same DL CC without a CIF. On the other hand, if the CIF is used byhigher-layer signaling, only DL CC ‘A’ may carry a PDCCH that schedulesa PDSCH in the same DL CC ‘A’ or another CC. Herein, no PDCCH istransmitted in DL CC ‘B’ and DL CC ‘C’ that are not configured as PDCCHmonitoring DL CCs.

1.3 Physical Downlink Control Channel (PDCCH)

1.3.1 PDCCH Overview

The PDCCH may deliver information about resource allocation and atransport format for a Downlink Shared Channel (DL-SCH) (i.e. a DLgrant), information about resource allocation and a transport format foran Uplink Shared Channel (UL-SCH) (i.e. a UL grant), paging informationof a Paging Channel (PCH), system information on the DL-SCH, informationabout resource allocation for a higher-layer control message such as arandom access response transmitted on the PDSCH, a set of Tx powercontrol commands for individual UEs of a UE group, Voice Over InternetProtocol (VoIP) activation indication information, etc.

A plurality of PDCCHs may be transmitted in the control region. A UE maymonitor a plurality of PDCCHs. A PDCCH is transmitted in an aggregate ofone or more consecutive Control Channel Elements (CCEs). A PDCCH made upof one or more consecutive CCEs may be transmitted in the control regionafter subblock interleaving. A CCE is a logical allocation unit used toprovide a PDCCH at a code rate based on the state of a radio channel. ACCE includes a plurality of RE Groups (REGs). The format of a PDCCH andthe number of available bits for the PDCCH are determined according tothe relationship between the number of CCEs and a code rate provided bythe CCEs.

1.3.2 PDCCH Structure

A plurality of PDCCHs for a plurality of UEs may be multiplexed andtransmitted in the control region. A PDCCH is made up of an aggregate ofone or more consecutive CCEs. A CCE is a unit of 9 REGs each REGincluding 4 REs. Four Quadrature Phase Shift Keying (QPSK) symbols aremapped to each REG. REs occupied by RSs are excluded from REGs. That is,the total number of REGs in an OFDM symbol may be changed depending onthe presence or absence of a cell-specific RS. The concept of an REG towhich four REs are mapped is also applicable to other DL controlchannels (e.g. the PCFICH or the PHICH). Let the number of REGs that arenot allocated to the PCFICH or the PHICH be denoted by N_(REG). Then thenumber of CCEs available to the system is N_(CCE) (=└N_(REG)/9┘) and theCCEs are indexed from 0 to NCCE-1.

To simplify the decoding process of a UE, a PDCCH format including nCCEs may start with a CCE having an index equal to a multiple of n. Thatis, given CCE i, the PDCCH format may start with a CCE satisfying i modn=0.

The eNB may configure a PDCCH with 1, 2, 4, or 8 CCEs. {1, 2, 4, 8} arecalled CCE aggregation levels. The number of CCEs used for transmissionof a PDCCH is determined according to a channel state by the eNB. Forexample, one CCE is sufficient for a PDCCH directed to a UE in a good DLchannel state (a UE near to the eNB). On the other hand, 8 CCEs may berequired for a PDCCH directed to a UE in a poor DL channel state (a UEat a cell edge) in order to ensure sufficient robustness.

[Table 2] below illustrates PDCCH formats. 4 PDCCH formats are supportedaccording to CCE aggregation levels as illustrated in [Table 2].

TABLE 2 Number of CCEs Number PDCCH format (n) Number of REGs of PDCCHbits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

A different CCE aggregation level is allocated to each UE because theformat or Modulation and Coding Scheme (MCS) level of controlinformation delivered in a PDCCH for the UE is different. An MCS leveldefines a code rate used for data coding and a modulation order. Anadaptive MCS level is used for link adaptation. In general, three orfour MCS levels may be considered for control channels carrying controlinformation.

Regarding the formats of control information, control informationtransmitted on a PDCCH is called DCI. The configuration of informationin PDCCH payload may be changed depending on the DCI format. The PDCCHpayload is information bits. [Table 3] lists DCI according to DCIformats.

TABLE 3 DCI Format Description Format 0 Resource grants for the PUSCHtransmissions (uplink) Format 1 Resource assignments for single codewordPDSCH transmissions (transmission modes 1, 2 and 7) Format 1A Compactsignaling of resource assignments for single codeword PDSCH (all modes)Format 1B Compact resource assignments for PDSCH using rank-1 closedloop precoding (mode 6) Format 1C Very compact resource assignments forPDSCH (e.g. paging/broadcast system information) Format 1D Compactresource assignments for PDSCH using multi-user MIMO (mode 5) Format 2Resource assignments for PDSCH for closed-loop MIMO operation (mode 4)Format 2A Resource assignments for PDSCH for open-loop MIMO operation(mode 3) Format 3/3A Power control commands for PUCCH and PUSCH with2-bit/1-bit power adjustment Format 4 Scheduling of PUSCH in one UL cellwith multi-antenna port transmission mode

Referring to [Table 3], the DCI formats include Format 0 for PUSCHscheduling, Format 1 for single-codeword PDSCH scheduling, Format 1A forcompact single-codeword PDSCH scheduling, Format 1C for very compactDL-SCH scheduling, Format 2 for PDSCH scheduling in a closed-loopspatial multiplexing mode, Format 2A for PDSCH scheduling in anopen-loop spatial multiplexing mode, and Format 3/3A for transmission ofTransmission Power Control (TPC) commands for uplink channels. DCIFormat 1A is available for PDSCH scheduling irrespective of thetransmission mode of a UE.

The length of PDCCH payload may vary with DCI formats. In addition, thetype and length of PDCCH payload may be changed depending on compact ornon-compact scheduling or the transmission mode of a UE.

The transmission mode of a UE may be configured for DL data reception ona PDSCH at the UE. For example, DL data carried on a PDSCH includesscheduled data, a paging message, a random access response, broadcastinformation on a BCCH, etc. for a UE. The DL data of the PDSCH isrelated to a DCI format signaled through a PDCCH. The transmission modemay be configured semi-statically for the UE by higher-layer signaling(e.g. Radio Resource Control (RRC) signaling). The transmission mode maybe classified as single antenna transmission or multi-antennatransmission.

A transmission mode is configured for a UE semi-statically byhigher-layer signaling. For example, multi-antenna transmission schememay include transmit diversity, open-loop or closed-loop spatialmultiplexing, Multi-User Multiple Input Multiple Output (MU-MIMO), orbeamforming. Transmit diversity increases transmission reliability bytransmitting the same data through multiple Tx antennas. Spatialmultiplexing enables high-speed data transmission without increasing asystem bandwidth by simultaneously transmitting different data throughmultiple Tx antennas. Beamforming is a technique of increasing theSignal to Interference plus Noise Ratio (SINR) of a signal by weightingmultiple antennas according to channel states.

A DCI format for a UE depends on the transmission mode of the UE. The UEhas a reference DCI format monitored according to the transmission modeconfigure for the UE. The following 10 transmission modes are availableto UEs:

-   -   Transmission mode 1: Single antenna transmission    -   Transmission mode 2: Transmission diversity    -   Transmission mode 3: Open-loop codebook based precoding when the        number of layer is greater than 1, Transmission diversity when        the number of rank is 1    -   Transmission mode 4: closed-loop codebook based precoding    -   Transmission mode 5: Multi-user MIMO of transmission mode 4        version    -   Transmission mode 6: closed-loop codebook based precoding which        is specifically limited for signal layer transmission    -   Transmission mode 7: precoding dose not based on codebooks only        supporting single layer transmission (release 8)    -   Transmission mode 8: precoding dose not based on codebooks        supporting maximum 2 layers (release 9)    -   Transmission mode 9: precoding dose not based on codebooks        supporting maximum 8 layers (release 10)    -   Transmission mode 10: precoding dose not based on codebooks        supporting maximum 8 layers, for CoMP use (release 11)

1.3.3 PDCCH Transmission

The eNB determines a PDCCH format according to DCI that will betransmitted to the UE and adds a Cyclic Redundancy Check (CRC) to thecontrol information. The CRC is masked by a unique Identifier (ID) (e.g.a Radio Network Temporary Identifier (RNTI)) according to the owner orusage of the PDCCH. If the PDCCH is destined for a specific UE, the CRCmay be masked by a unique ID (e.g. a cell-RNTI (C-RNTI)) of the UE. Ifthe PDCCH carries a paging message, the CRC of the PDCCH may be maskedby a paging indicator ID (e.g. a Paging-RNTI (P-RNTI)). If the PDCCHcarries system information, particularly, a System Information Block(SIB), its CRC may be masked by a system information ID (e.g. a SystemInformation RNTI (SI-RNTI)). To indicate that the PDCCH carries a randomaccess response to a random access preamble transmitted by a UE, its CRCmay be masked by a Random Access-RNTI (RA-RNTI).

Then the eNB generates coded data by channel-encoding the CRC-addedcontrol information. The channel coding may be performed at a code ratecorresponding to an MCS level. The eNB rate-matches the coded dataaccording to a CCE aggregation level allocated to a PDCCH format andgenerates modulation symbols by modulating the coded data. Herein, amodulation order corresponding to the MCS level may be used for themodulation. The CCE aggregation level for the modulation symbols of aPDCCH may be one of 1, 2, 4, and 8. Subsequently, the eNB maps themodulation symbols to physical REs (i.e. CCE to RE mapping).

1.4 Reference Signal (RS)

Hereinafter, reference signals are explained, which are used for theembodiments of the present invention.

FIG. 7 illustrates a subframe to which cell specific reference signals(CRSs) are allocated, which may be used in embodiments of the presentdisclosure.

FIG. 7 represents an allocation structure of the CRS in case of thesystem supporting 4 antennas. Since CRSs are used for both demodulationand measurement, the CRSs are transmitted in all DL subframes in a cellsupporting PDSCH transmission and are transmitted through all antennaports configured at an eNB.

More specifically, CRS sequence is mapped to complex-modulation symbolsused as reference symbols for antenna port p in slot n_(s).

A UE may measure CSI using the CRSs and demodulate a signal received ona PDSCH in a subframe including the CRSs. That is, the eNB transmits theCRSs at predetermined locations in each RB of all RBs and the UEperforms channel estimation based on the CRSs and detects the PDSCH. Forexample, the UE may measure a signal received on a CRS RE and detect aPDSCH signal from an RE to which the PDSCH is mapped using the measuredsignal and using the ratio of reception energy per CRS RE to receptionenergy per PDSCH mapped RE.

When the PDSCH is transmitted based on the CRSs, since the eNB shouldtransmit the CRSs in all RBs, unnecessary RS overhead occurs. To solvesuch a problem, in a 3GPP LTE-A system, a UE-specific RS (hereinafter,UE-RS) and a CSI-RS are further defined in addition to a CRS. The UE-RSis used for demodulation and the CSI-RS is used to derive CSI. The UE-RSis one type of a DRS.

Since the UE-RS and the CRS may be used for demodulation, the UE-RS andthe CRS can be regarded as demodulation RSs in terms of usage. Since theCSI-RS and the CRS are used for channel measurement or channelestimation, the CSI-RS and the CRS can be regarded as measurement RSs.

FIG. 8 illustrates channel state information reference signal (CSI-RS)configurations allocated according to the number of antenna ports, whichmay be used in embodiments of the present disclosure.

A CSI-RS is a DL RS that is introduced in a 3GPP LTE-A system forchannel measurement rather than for demodulation. In the 3GPP LTE-Asystem, a plurality of CSI-RS configurations is defined for CSI-RStransmission. In subframes in which CSI-RS transmission is configured,CSI-RS sequence is mapped to complex modulation symbols used as RSs onantenna port p.

FIG. 8( a) illustrates 20 CSI-RS configurations 0 to 19 available forCSI-RS transmission through two CSI-RS ports among the CSI-RSconfigurations, FIG. 8( b) illustrates 10 available CSI-RSconfigurations 0 to 9 through four CSI-RS ports among the CSI-RSconfigurations, and FIG. 8( c) illustrates 5 available CSI-RSconfigurations 0 to 4 through 8 CSI-RS ports among the CSI-RSconfigurations.

The CSI-RS ports refer to antenna ports configured for CSI-RStransmission. Since CSI-RS configuration differs according to the numberof CSI-RS ports, if the numbers of antenna ports configured for CSI-RStransmission differ, the same CSI-RS configuration number may correspondto different CSI-RS configurations.

Unlike a CRS configured to be transmitted in every subframe, a CSI-RS isconfigured to be transmitted at a prescribed period corresponding to aplurality of subframes. Accordingly, CSI-RS configurations vary not onlywith the locations of REs occupied by CSI-RSs in an RB pair according toTable 6 or Table 7 but also with subframes in which CSI-RSs areconfigured.

Meanwhile, if subframes for CSI-RS transmission differ even when CSI-RSconfiguration numbers are the same, CSI-RS configurations also differ.For example, if CSI-RS transmission periods (T_(CSI-RS)) differ or ifstart subframes (Δ_(CSI-RS)) in which CSI-RS transmission is configuredin one radio frame differ, this may be considered as different CSI-RSconfigurations.

Hereinafter, in order to distinguish between a CSI-RS configuration towhich (1) a CSI-RS configuration is assigned and (2) a CSI-RSconfiguration varying according to a CSI-RS configuration number, thenumber of CSI-RS ports, and/or a CSI-RS configured subframe, the CSI-RSconfiguration of the latter will be referred to as a CSI-RS resourceconfiguration. The CSI-RS configuration of the former will be referredto as a CSI-RS configuration or CSI-RS pattern.

Upon informing a UE of the CSI-RS resource configuration, an eNB mayinform the UE of information about the number of antenna ports used fortransmission of CSI-RSs, a CSI-RS pattern, CSI-RS subframe configurationI_(CSI-RS), UE assumption on reference PDSCH transmitted power for CSIfeedback P_(c), a zero-power CSI-RS configuration list, a zero-powerCSI-RS subframe configuration, etc.

CSI-RS subframe configuration I_(CSI-RS) is information for specifyingsubframe configuration periodicity T_(CSI-RS) and subframe offsetΔ_(CSI-RS) regarding occurrence of the CSI-RSs. The following table 8shows CSI-RS subframe configuration I_(CSI-RS) according to TCSI-RS andΔCSI-RS.

TABLE 8 CSI-RS CSI-RS subframe offset CSI-RS-SubframeConfig periodicityTCSI-RS ΔCSI-RS ICSI-RS (subframes) (subframes) 0-4 5 ICSI-RS  5-14 10ICSI-RS-5 15-34 20 ICSI-RS-15 35-74 40 ICSI-RS-35  75-154 80 ICSI-RS-75

Subframes satisfying the following Equation 1 are subframes includingCSI-RSs.

(10n _(f) +└n _(s)/2┘−Δ_(CSI-RS))mod T _(CSI-RS)=0  [Equation 1]

A UE configured as transmission modes defined after introduction of the3GPP LTE-A system (e.g. transmission mode 9 or other newly definedtransmission modes) may perform channel measurement using a CSI-RS anddecode a PDSCH using a UE-RS.

FIG. 9 illustrates an example of a subframe to which UE-RSs areallocated, which may be used in embodiments of the present disclosure.

Referring to FIG. 9, the subframe illustrates REs occupied by UE-RSsamong REs in one RB of a normal DL subframe having a normal CP.

UE-RSs are transmitted on antenna port(s) p=5, p=7, p=8 or p=7, 8, . . ., ν+6 for PDSCH transmission, where u is the number of layers used forthe PDSCH transmission. UE-RSs are present and are a valid reference forPDSCH demodulation only if the PDSCH transmission is associated with thecorresponding antenna port. UE-RSs are transmitted only on RBs to whichthe corresponding PDSCH is mapped.

The UE-RSs are configured to be transmitted only on RB(s) to which aPDSCH is mapped in a subframe in which the PDSCH is scheduled unlikeCRSs configured to be transmitted in every subframe irrespective ofwhether the PDSCH is present. Accordingly, overhead of the RS maydecrease relative to overhead of the CRS.

In the 3GPP LTE-A system, the UE-RSs are defined in a PRB pair.Referring to FIG. 9, in a PRB having frequency-domain index nPRBassigned for PDSCH transmission with respect to p=7, p=8, or p=7, 8, . .. , ν+6, a part of UE-RS sequence r(m) is mapped to complex-valuedmodulation symbols a_(k,l) ^((p)) in a subframe according to thefollowing equation 10.

UE-RSs are transmitted through antenna port(s) correspondingrespectively to layer(s) of a PDSCH. That is, the number of UE-RS portsis proportional to a transmission rank of the PDSCH. Meanwhile, if thenumber of layers is 1 or 2, 12 REs per RB pair are used for UE-RStransmission and, if the number of layers is greater than 2, 24 REs perRB pair are used for UE-RS transmission. In addition, locations of REsoccupied by UE-RSs (i.e. locations of UE-RS REs) in a RB pair are thesame with respect to a UE-RS port regardless of a UE or a cell.

As a result, the number of DMRS REs in an RB to which a PDSCH for aspecific UE in a specific subframe is mapped is the same. Notably, inRBs to which the PDSCH for different UEs in the same subframe isallocated, the number of DMRS REs included in the RBs may differaccording to the number of transmitted layers.

1.5 Synchronization Signal

A Synchronization Signal (SS) is categorized into a PrimarySynchronization Signal (PSS) and a Secondary Synchronization Signal(SSS). The SS is a signal used for synchronization acquisition and cellsearch between a UE and an eNB.

FIG. 10 illustrates an example of a frame structure in which SStransmission positions are indicated. Particularly, FIG. 10( a) and FIG.10( b) illustrate frame structures for SS transmission in systems usinga normal Cyclic Prefix (CP) and an extended CP, respectively.

An SS is transmitted in the second slot of subframe number 0 and thesecond slot of subframe number 5, in consideration of a GSM frame lengthof 4.6 ms for facilitation of inter-Radio Access Technology (RAT)measurement. A boundary of the corresponding radio frame may be detectedthrough an SSS.

Referring to FIG. 10( a) and FIG. 10( b), a PSS is transmitted on thelast OFDM symbols of slot numbers 0 and 5 and an SSS is transmitted onan OFDM symbol immediately before the PSS. The SS may transmit a totalof 504 physical cell IDs by a combination of 3 PSSs and 168 SSSs. Inaddition, the SS and a PBCH are transmitted within middle 6 RBs of asystem bandwidth so that the UE may detect or decode the SS and PBCHirrespective of the size of a transmission bandwidth.

A transmit diversity scheme of the SS uses only a single antenna port.That is, a single antenna transmission scheme or a UE transparenttransmission scheme (e.g. Precoding Vector Switching (PVS), TimeSwitched Transmit Diversity (TSTD), or Cyclic Delay Diversity (CDD)) maybe used.

1.5.1 Primary Synchronization Signal (PSS)

A length-63 Zadoff-Chu (ZC) sequence is defined in the frequency domainand is used as a sequence of the PSS. The ZC sequence is defined byEquation 2.

$\begin{matrix}{{d_{u}(n)} = ^{{- j}\frac{\pi \; {{un}{({n + 1})}}}{N_{ZC}}}} & \lbrack {{Equation}\mspace{14mu} 2} \rbrack\end{matrix}$

In Equation 2, Nzc represents length-63 of the ZC sequence and du(n)represents a PSS sequence according to a root index u. A sequenceelement corresponding to a Direct Current (DC) subcarrier, n=31, ispunctured.

Among middle 6 RBs (=72 subcarriers) of bandwidth, 9 remainingsubcarriers carry a value of always 0 to facilitate filter design forperforming synchronization. To define a total of three PSSs, values ofu=25, 29, and 34 may be used in Equation 2. In this case, since u=29 andu=34 have a conjugate symmetry relation, two correlations may besimultaneously performed. Here, conjugate symmetry indicates therelationship of the following Equation 3. A one-shot correlator for u=29and u=34 may be implemented using the characteristics of conjugatesymmetry so that the entire amount of calculation can be reduced byabout 33.3%.

d _(u)(n)=(−1)^(n)(d _(N) _(ZC) _(−u)(n))*, when N _(ZC) is even number.

d _(u)(n)=(d _(N) _(ZC) _(−u)(n))*, when N _(ZC) is oddnumber.  [Equation 3]

1.5.2 Secondary Synchronization Signal (SSS)

An SSS is generated by interleaving and concatenating two m-sequences oflength-31. In this case, 168 cell group IDs may be identified bycombining the two sequences. As the sequence of the SSS, the m-sequencesare robust in a frequency selective environment and can reduce theamount of calculation by high-speed m-sequence transform using fastHadamard transform. In addition, configuration of the SSS using twoshort codes has been proposed to reduce the amount of calculation by aUE.

FIG. 11 illustrates an SSS generation method.

Referring to FIG. 11, it may be appreciated that two m-sequences definedin a logical region are interleaved and mapped in a physical region. Forexample, if two m-sequences used to generate an SSS code are defined asS1 and S2, when the SSS of subframe index 0 transmits a cell group ID bya combination of the two sequences of (S1, S2), the SSS of subframeindex 5 transmits the cell group ID by swapping the sequences for (S2,S1), so that a boundary of a 10 ms frame can be distinguished. The SSScode used in this case is generated using a polynomial of x⁵+x²+1 and atotal of 31 codes may be generated through different circular shifts.

To improve reception performance, two different PSS based sequences aredefined and are scrambled to the SSS. Here, the PSS based sequences arescrambled to S1 and S2 as different sequences. Next, an S1 basedscrambling code is defined and is scrambled to S2. In this case, SSScodes are swapped in units of 5 ms but PSS based scrambling codes arenot swapped. The PSS based scrambling code is defined as 6 cyclic shiftversions according to a PSS index in an m-sequence generated from apolynomial of x⁵+x³+1 and the S1 based scrambling code is defined as 8cyclic shift versions according to an S1 index in an m-sequencegenerated from a polynomial of x⁵+x⁴+x²+x¹+1.

2. PQI and QCL used in NCT

2.1 New Carrier Type (NCT)

In LTE Release 8/9/10/11 systems which are legacy systems, RSs andcontrol channels such as a CRS, a Primary Synchronization Signal (PSS),a Secondary Synchronization Signal (SSS), a PDCCH, and a PBCH aretransmitted in a DL CC.

However, in a future wireless access system, a DL CC in which all orsome of the CRS, the PSS/SSS, the PDCCH, and the PBCH are nottransmitted may be introduced in order to overcome an interferenceproblem between a plurality of cells and to improve carrier extension.In the embodiments of the present disclosure, this carrier is defined asan extension carrier or a New Carrier Type (NCT), for convenience.

The NCT described in the present disclosure may be an SCell in the casein which an eNB supports CA or may be a carrier or a serving cellprovided by a neighboring eNB for cooperative data transmission in thecase in which eNBs support CoMP. In addition, the NCT may be a smallcell which is a cell synchronized with a reference cell (e.g. PCell).

2.2 Quasi Co-Location (QCL)

Hereinafter, QCL between antenna ports will be described.

If antenna ports are Quasi-Co-Located (also called QCL), this means that“a UE may assume that large-scale properties of a signal received fromone antenna port (or a radio channel corresponding to one antenna port)are equal in entirety or in part to large-scale properties of a signalreceived from another antenna port (or a radio channel corresponding toanother antenna port)”. The large-scale properties may include Dopplerspread related to a frequency offset, Doppler shift, an average delayrelated to a timing offset, and a delay spread and may further includean average gain.

According to definition of QCL, the UE cannot assume that thelarge-scale properties of antenna ports not in a QCL relationship, i.e.large-scale properties of Non Quasi Co-Located (NQCL) antenna ports areequal. In this case, the UE should independently perform a trackingprocedure to obtain the frequency offset, the timing offset, etc.according to an antenna port.

In contrast, the UE may advantageously perform following operationsbetween QCL antenna ports.

1) The UE may identically apply a power-delay profile, delay spread, aDoppler spectrum, and Doppler spread estimation result, for a radiochannel corresponding to a specific antenna port, to Wiener filterparameters, etc. which are used to estimate a radio channelcorresponding to another antenna port.

2) The UE may acquire time synchronization and frequency synchronizationfor the specific antenna port and then apply the same synchronization toanother antenna port.

3) The UE may calculate a Reference Signal Received Power (RSRP)measurement value of each QCL antenna port as an average with respect toaverage gain.

For example, when the UE receives scheduling information (e.g. DCIformat 2C) about a DeModulation Reference Signal (DM-RS) based DL datachannel via a PDCCH (or an E-PDCCH), it is assumed that the UE performschannel estimation for a PDSCH via a DM-RS sequence indicated by thescheduling information and then performs data demodulation.

In this case, if a DM-RS antenna port for DL data channel demodulationis QCL with a CRS antenna port of a serving cell, the UE may applyinglarge-scale properties of a radio channel estimated from a CRS antennaport thereof without change upon channel estimation via the DM-RSantenna port, thereby improving reception performance of the DM-RS basedDL data channel.

Similarly, if a DM-RS antenna port used for DL data channel demodulationis QCL with a CSI-RS antenna port of a serving cell, the UE may applylarge-scale properties of a radio channel estimated from the CSI-RSantenna port of the serving cell without change upon channel estimationvia the DM-RS antenna port, thereby improving reception performance ofthe DM-RS based DL data channel.

Meanwhile, an LTE system defines that an eNB sets one of QCL type A andQCL type B with respect to a UE via a higher layer signal upontransmitting a DL signal in transmission mode 10, which is a CoMP mode.

In QCL type A, it is assumed that antenna ports of a CRS, a DM-RS, and aCSI-RS are QCL with respect to large-scale properties except for averagegain and the same node transmits physical channels and signals.

In contrast, in QCL type B, up to four QCL modes for each UE are set viaa higher layer message so as to perform CoMP transmission such asDynamic Point Selection (DPS) or Joint Transmission (JT) and a QCL modeto be used for DL signal reception among the four QCL modes is definedto be dynamically set through a PQI field of DCI.

DPS transmission in the case of QCL type B will now be described in moredetail.

First, it is assumed that node #1 composed of N1 antenna ports transmitsCSI-RS resource #1 and node #2 composed of N2 antenna ports transmitsCSI-RS resource #2. In this case, CSI-RS resource #1 is included in QCLmode parameter set #1 and CSI-RS resource #2 is included in QCL modeparameter set #2. The eNB sets parameter set #1 and parameter set #2 viaa higher layer signal with respect to a UE located within commoncoverage of node #1 and node #2.

Next, the eNB may perform DPS by setting parameter set #1 using DCI upondata (i.e. PDSCH) transmission to the UE via node #1 and settingparameter set #2 upon data transmission to the UE via node #2. If the UEmay assume that CSI-RS resource #1 and a DM-RS are QCL upon receivingparameter set #1 via the DCI and that CSI-RS resource #2 and the DM-RSare QCL upon receiving parameter set #2.

2.2.1 DCI Format 2D

DCI format 2D has been newly defined to support DL transmission in anLTE-A Rel-11 system. In particular, DCI format 2D is defined to supportCoMP between eNBs and is associated with transmission mode 10. That is,in order for a UE configured as transmission mode 10 for an allocatedserving cell to decode a PDSCH according to a detected PDCCH/EPDCCHsignal with DCI format 2D, up to 4 parameter sets may be configuredthrough higher layer signaling. For a detailed description of each fieldincluded in DCI format 2D, reference may be made to section 5.3.3.1.5Dof 3GPP TS 36.212 v11.3.

Table 5 shown below shows an exemplary PDSCH RE Mapping andQuasi-Co-Location Indicator (PQI) field included in DCI format 2D.

TABLE 5 Value of ‘PDSCH RE Mapping and Quasi-Co-Location Indicator’field Description ‘00’ Parameter set 1 configured by higher layers ‘01’Parameter set 2 configured by higher layers ‘10’ Parameter set 3configured by higher layers ‘11’ Parameter set 4 configured by higherlayers

Parameters shown in the following Table 6 are used to determine PDSCH REmapping and PDSCH antenna port QCL. In Table 5, the PQI field indicateseach parameter set configured via higher layer signaling.

TABLE 6 Parameter Description crs-PortsCount-r11 Number of CRS antennaports for DPSCH RE mapping crs-FreqShift-r11 CRS frequency shift forPDSCH RE mapping mbsfn-SubframeConfigList-r11 MBSFN subframeconfiguration for PDSCH RE mapping csi-RS-ConfigZPId-r11 Zero-powerCSI-RS resource configuration for PDSCH RE mapping pdsch-Start-r11 PDSCHstarting position for PDSCH RE mapping qcl-CSI-RS-ConfigNZPId-r11 CSI-RSresource configuration identity for Quasi-Co-Location

Referring to Table 6, parameter ‘crs-PortsCount-r11’ represents thenumber of CRS antenna ports for PDSCH RE mapping, parameter‘crs-FreqShift-r11’ represents a CRS frequency shift value for PDSCH REmapping, and parameter ‘mbsfn-SubframeConfigList-r11’ represents aMultimedia Broadcast over Single Frequency Network (MBSFN) subframeconfiguration for PDSCH RE mapping. In addition, parameter‘csi-RS-ConfigZPId-r11’ represents a zero-power CSI-RS resourceconfiguration for PDSCH RE mapping, parameter ‘pdsch-Start-r11’represents a PDSCH start position for PDSCH RE mapping, and parameter‘qcl-CSI-RS-ConfigNZPId-r11’ is used to identify a CSI-RS resourceconfiguration for QCL.

In Table 5, parameter sets 1, 2, 3, and 4 are composed of a combinationof the parameters shown in Table 6. Information about the combination ofthe parameters included in each parameter set is signaled to the UE by ahigher layer.

2.3 Definition of New PQI Used in NCT

A legacy system supports transmission of a CRS, a PDCCH, etc., whereas anext system introduces an NCT in which transmission of the CRS, thePDCCH, etc. is not supported to raise data transmission efficiency. Inthe NCT, a new RS which is mapped to an RE corresponding to an antennaport of the CRS used in the legacy system but is not used fordemodulation is defined. For example, since the new RS is used only fortime/frequency tracking (i.e. time/frequency synchronizationacquisition), the new RS will be referred to as a Tracking ReferenceSignal (TRS) in the embodiments of the present disclosure.

The TRS may be periodically transmitted in the NCT (e.g. at an intervalof 5 ms). In an LTE Rel-11 system, Transmission Mode (TM) 10 is definedto support a CoMP operation. In this case, PQI information is includedin DCI format 2D for PDSCH rate matching. The PQI information indicates4 states using two bits (refer to section 1.4) and each state representsa combination of information configured by a higher layer.

In the NCT, not the CRS but the TRS is periodically transmitted on an REcorresponding to an antenna port of the CRS. Accordingly, theembodiments of the present disclosure provide a method for newlyconfiguring and interpreting the PQI information used in the NCT.Particularly, the PQI information may be reconfigured as an abbreviatedtype suitable for the NCT.

3. Radio Resource Measurement (RRM)

When CA is supported in a wireless access system, each carrier (i.e.serving cell) may schedule a PDSCH/PUSCH through a PDCCH using aself-scheduling scheme. Alternatively, each carrier may schedule aPDSCH/PUSCH of another serving cell through a PDCCH transmitted in anyone serving cell using cross carrier scheduling (refer to section 1.2).In the embodiments of the disclosure, the term carrier used in CA hasthe same meaning as serving cell.

In order to add any serving cell to CA as a secondary carrier or asecondary serving cell, a UE needs to perform neighbor cell measurement.Generally, neighbor cell measurement is performed using a CRS and mayalso be called RRM.

Carriers (i.e. serving cells) included in a CA set are divided intosynchronized carriers and non-synchronized carriers.

A non-synchronized carrier refers to a carrier that assumes itself to bea synchronization reference carrier for synchronization. That is, sincesynchronization signals (e.g. PSS/SSS etc.) necessary forsynchronization acquisition are transmitted in the non-synchronizedcarrier, the UE may autonomously secure synchronization in thenon-synchronized carrier.

In contrast, synchronization signals necessary for synchronizationacquisition are not transmitted in a synchronized carrier. Instead, thesynchronized carrier may set a neighbor carrier (or serving cell) of thesame frequency band having similar propagation characteristics andsimilar channel characteristics as a synchronization reference carrier(or reference cell) and use synchronization information of the referencecarrier as synchronization information thereof. That is, thesynchronized carrier is synchronized with a carrier other than itselfand refers to a carrier that assumes other carriers to besynchronization reference carriers for synchronization acquisition.

For synchronization acquisition in the synchronized carrier, the UE mayperform synchronization tracking for the synchronized carrier byreceiving a radio signal (e.g. a PSS, an SSS, or an RS) of thesynchronization reference carrier during a specific time duration (e.g.a specific subframe having a specific period) in the synchronizedcarrier. In this case, the UE may be configured to stop operationsrelated to DL data/signal reception etc. in the synchronized carrierduring the time duration.

The UE may perform not only synchronization acquisition and maintenancefor the synchronization reference carrier but also Reference SignalReceived Power (RSRP) measurement, Reference Signal Received Quality(RSRQ) measurement, or Path Loss (PL) measurement for thesynchronization reference carrier.

In the embodiments of the present disclosure, the synchronized carriermay have the same meaning as a synchronized serving cell, a synchronizedcell, a New Carrier Type (NCT), or a first cell. In addition, thenon-synchronized carrier may be used as the same meaning as asynchronization reference carrier, a synchronization carrier, asynchronization reference serving cell, a synchronization referencecell, or a second cell.

3.1 RRM Method-1

FIG. 12 illustrates an example of an RRM method.

Referring to FIG. 12, it is assumed that an eNB manages two or morecells including a first cell and a second cell. It is also assumed thata UE operates in the first cell which is a synchronized carrier and thesecond cell is a synchronization reference carrier.

The UE operating in the first cell may acquire and maintainsynchronization in the first cell by receiving a PSS, an SSS, and/or anRS transmitted in the second cell which is the synchronization referencecarrier during a prescribed subframe duration (S1210 and S1220).

To acquire synchronization of the first cell from the second cell, thefirst cell and the second cell desirably have similar frequencycharacteristics. Therefore, when CoMP is supported, neighbor cells maybe the first cell and the second cell. When QCL is supported, cellswhich are positioned at the same geographic location may be the firstcell and the second cell.

The UE may perform RRM for the first cell by receiving a CRS and/or aCSI-RS transmitted in the second cell (S1240).

3.2 RRM Method-2

FIG. 13 illustrates another example of an RRM method.

It is assumed that an eNB manages two or more cells including a firstcell and a second cell. It is also assumed that a UE operates in thefirst cell which is a synchronized carrier and the second cell is asynchronization reference carrier. The UE operating in the first cellmay maintain synchronization using the second cell and perform RRM usinga CSI-RS or a CRS of the first cell.

Hereinafter, the case in which the first cell and the second cell inFIG. 13 are configured as a QCL relationship (refer to section 2.2) willbe described.

Referring to FIG. 13, the UE operating in the first cell may maintainsynchronization for the first cell using a synchronization signal(PSS/SSS) of the second cell (S1310 and S1320).

The eNB may transmit information related to QCL between the first celland the second cell through a PCell via higher layer signaling. If thesecond cell, which is the synchronization reference cell, is the PCell,the UE may receive the QCL related information from the second cell(S1330).

Since it is assumed that the first cell and the second cell are QCL, theUE may receive a CRS and/or a CSI-RS transmitted in the second cell anduse the received CRS and/or CSI-RS for RRM for the first cell (S1340 andS1360).

Namely, the UE may perform RRM under the assumption that the CSI-RS ofthe first cell and the CRS and/or CSI-RS of the second cell are QCL.

Alternatively, if the first cell and the second cell are QCL, the UE mayassume that the CSI-RS of the first cell and the CRS and/or CSI-RS ofthe second cell are QCL. Accordingly, the UE can improve receptionperformance of a CSI-RS based DL data channel of the first cell uponreceiving the CSI-RS of the first cell by applying large-scaleproperties obtained upon reception of the CRS and/or the CSI-RS of thesecond cell. (S1350).

Alternatively, the UE may receive the CSI-RS of the first cell based onthe large-scale properties obtained through the CRS and/or the CSI-RS ofthe second cell with which the CSI-RS of the first cell is QCL. Inaddition, the UE may perform RRM for the first cell using the CSI-RS ofthe first cell.

Next, the UE may transmit a measurement report message including an RRMresult to the PCell of the eNB (S1370).

3.3 RRM Method-3

FIG. 14 illustrates another example of an RRM method.

It is assumed that an eNB manages two or more cells including a firstcell and a second cell. It is also assumed that a UE operates in thefirst cell which is a synchronized carrier and the second cell is asynchronization reference carrier. The UE operating in the first cellmay maintain synchronization and perform RRM using the second cell andsimultaneously perform RRM using a CSI-RS or a CRS of the first cell.

Hereinafter, the case in which the first cell and the second cell inFIG. 14 are configured as QCL (refer to section 2.2) will be described.That is, if the first cell and the second cell are configured as QCL,the UE may perform RRM under the assumption that the CSI-RS of the firstcell and a CRS and/or a CSI-RS of the second cell are QCL. In this case,the UE operating in the first cell may maintain synchronization for thefirst cell using a synchronization signal (PSS/SSS) of the second cell.

Referring to FIG. 14, the eNB may transmit information related to QCLbetween the first cell and the second cell through a PCell via higherlayer signaling. If the second cell which is the synchronizationreference cell is the PCell, the UE may receive the QCL relatedinformation from the second cell (S1410).

Since it is assumed that the first cell and the second cell are QCL, theUE may receive the CRS and/or the CSI-RS transmitted in the second celland perform RRM for the first cell (S1420 and S1430).

The UE may acquire large-scale properties through the CRS and/or theCSI-RS received from the second cell and apply the large-scaleproperties upon receiving the CSI-RS from the first cell (S1440).

Namely, the UE may perform RRM using the CSI-RS received from the firstcell (S1450).

In FIG. 14, the UE may separately feed back RRM values measured in stepsS1430 and S1450 or may feed back an average of the RRM values to thePCell of the eNB. In other words, the UE may transmit a measurementreport message including an RRM result to the PCell of the eNB (S1460).

3.4 RRM Method-4

Another embodiment which is different from the above scheme describedwith reference to FIG. 14 will now be described. In this case, a basicpremise is identical to the above description of FIG. 14.

Notably, in step S1430, the UE may perform only either RSRP measurementor RSRP and PL measurement out of RRM. In this case, in step S1450,either RSRQ measurement or RSRQ and PL measurement which is notperformed in step S1430 may be performed.

That is, the UE may perform RSRQ measurement or RSRQ and PL measurementthrough the first cell and perform RSRP measurement or RPRQ and PLmeasurement for the first cell through the second cell which is QCL withthe first cell.

3.5 RRM Method-5

Another embodiment which is different from the above scheme describedwith reference to FIG. 14 will now be described. In this case, a basicpremise is identical to the above description of FIG. 14.

The UE operating in the first cell may maintain synchronization usingthe second cell, perform RSRP measurement using a CRS and/or a CSI-RStransmitted in the second cell, and perform interference measurement forRSRQ measurement using a CSI-RS transmitted in the first cell. That is,the UE may perform RSRQ measurement using values obtained from differentcells as values for calculating RSRQ. In this case, the UE may performPL measurement using the CRS/CSI-RS transmitted in the second cell orusing a CSI-RS transmitted in the first cell.

Alternatively, the UE may perform RRM under the assumption that theCSI-RS of the first cell and the CRS and/or CSI-RS of the second cellare QCL.

As described in sections 3.1 to 3.5, when antenna ports used in thefirst cell and the second cell are QCL, the UE may use the CRS and/orthe CSI-RS of the second cell for RRM of the first cell.

As another aspect of the present invention, the UE may be configured toselect an RS used for RRM according to a QCL assumption. For example,information about QCL of the CSI-RS (or a DM-RS) of the first cell andthe CRS and/or the CSI-RS of the second cell may be indicated to the UEvia higher layer signaling. In this case, the UE may perform RRM of thefirst cell using the CRS/CSI-RS of the second cell.

Alternatively, if the information about QCL of the CSI-RS of the firstcell and the CRS/CSI-RS of the second cell is not transmitted via higherlayer signaling, the UE may perform RRM for the first cell using theCSI-RS of the first cell. For instance, if the QCL information is nottransmitted in FIG. 12, the UE may maintain synchronization through thesecond cell and perform RRM using the CSI-RS of the first cell.

As another aspect of the present invention, if the CSI-RS (or DM-RS) ofthe first cell is configured to be QCL with a TRS of the first cell, theUE may perform RRM using the TRS of the first cell.

If a QCL relationship between the CSI-RS of the first cell and anotherRS is not defined for the UE (behavior B without associated indicatedCRS), the UE may assume that the NCT of the first cell transmits theTRS.

In the embodiments of the present invention, the UE needs to acquire acell ID of a measurement target cell and acquire synchronization inorder to perform RRM. Therefore, a synchronization reference cell of thefirst cell may be selected from among measurable cells. In contrast, fora cell (i.e. the second cell) designated as the synchronizationreference cell of the first cell, the UE should perform cellmeasurement. In addition, measurement of the first cell may beconfigured to be performed with respect to the synchronization referencecell (i.e. the second cell).

4. Method for Adding Synchronized Cell to CA Set

In order to aggregate a synchronized cell (i.e. first cell) to a CA setas an SCell, the UE needs first to perform an RRM procedure or a cellmeasurement procedure. However, since the first cell does not transmit asynchronization related signal (e.g. a PSS/SSS, a CRS, etc.), the UEcannot directly perform RRM for the first cell.

Therefore, the UE may determine whether to aggregate the first cell tothe CA set as the SCell by measuring the second cell instead of thefirst cell. In this case, the eNB may configure or activate the firstcell as the SCell according to a measurement result for the second cellby the UE as in the following methods.

(1) Method 1: The first cell is independently configured and activated.

(2) Method 2: The first cell and the second cell are simultaneouslyconfigured.

(3) Method 2-1: The first cell and the second cell are simultaneouslyconfigured and the first cell and the second cell are independentlyactivated.

(4) Method 2-2: The first cell and the second cell are simultaneouslyconfigured and the first cell and the second cell are always activatedat the same time.

In addition, when the first cell is configured and/or activated as theSCell, the eNB may inform the UE that a corresponding cell is the firstcell. Alternatively, the eNB may transmit information about the firstcell upon directing the UE to perform RRM for the first cell.

4.1 Definition of CP for First Cell and Second Cell

When the first cell, which is a synchronized cell, and the second cell,which is a synchronization reference cell, are configured together, amethod for setting the length of a CP will now be described.

When a CP length applied to the second cell is set to be longer than aCP length applied to the first cell, even if the UE acquires timingsynchronization in the second cell, it cannot be ensured whethercorresponding timing synchronization is equally applied to the firstcell. Therefore, methods for setting the CP length applicable to thefirst cell and the second cell are as follows.

(1) Method A: The second cell has a normal CP length and the first cellhas a normal CP length.

(2) Method B: The second cell has a normal CP length and the first cellhas an extended CP length.

(3) Method C: The second cell has an extended CP length and the firstcell has an extended CP length.

In this case, a characteristic configuration is that the CP length ofthe second cell and the CP length of the first cell are identically set.That is, Method A or Method C is desirable.

4.2 Definition of Cell ID for First Cell

As described in section 1.5, a maximum number of cell IDs managed by theeNB may be 504. In this case, as the number of serving cells allocatedto each UE increases due to CA and an NCT is introduced, the cell IDsmay be insufficient. Accordingly, a method for solving problems of celldeployment, which may be caused by cell ID shortage, will be describedbelow.

If the second cell, which is a synchronization reference cell, and thefirst cell, which is a synchronized cell are configured together andactivated, an independent cell ID may not be assigned to the first cell.For example, initialization of scrambling sequences of a PDSCH, a DM-RS,and a CSI-RS using cell IDs as parameters may be performed such that thesecond cell and the first cell are initialized to the same value usingthe same parameter.

In more detail, initialization of a scrambling sequence of a PDSCHcorresponding to a q-th (where qε{0,1}) codeword used to initialize ascrambling sequence of a PDSCH transmitted in the first cell may beexpressed by Equation 4.

$\begin{matrix}{c_{init} = \{ {{n_{RNTI} \cdot 2^{14}} + {q \cdot 2^{13}} + {\lfloor {n_{s}/2} \rfloor \cdot 2^{9}} + {A\mspace{14mu} {for}{\mspace{11mu} \;}{PDSCH}}} } & \lbrack {{Equation}\mspace{14mu} 4} \rbrack\end{matrix}$

In Equation 4, A denotes a value corresponding to a cell ID of thesecond cell, a value corresponding to a PCell ID, or a unique value setby a higher layer to replace a cell ID.

By applying the same principle, initialization of a scrambling sequenceof a DM-RS used in the first cell may be expressed by Equation 5.

c _(init)=(└n _(s)/2┘+1)·(B+1)·2¹⁶ +n _(SCID)  [Equation 5]

In Equation 5, B denotes a value corresponding to a cell ID of thesecond cell, a value corresponding to a PCell ID, or a unique value setby a higher layer to replace a cell ID.

By applying the same principle, initialization of a scrambling sequenceof a CSI-RS used in the first cell may be expressed by Equation 6.

c _(init)=2¹⁰·(7·(n _(s)+1)+l+1)·(2·C+1)+2·C+N _(CP)  [Equation 6]

In Equation 6, C denotes a value corresponding to a cell ID of thesecond cell, a value corresponding to a PCell ID, or a unique value setby a higher layer to replace a cell ID.

4.3 Out-of-Synchronization

4.3.1 Definition of Out-of-Synchronization in LTE System

In the LTE system, out-of-synchronization is defined as follows.

(1) The UE should monitor DL quality based on a CRS in order to detectDL radio link quality of a PCell.

(2) The UE should estimate DL radio link quality and compare the radiolink quality with threshold values Q_(out) and Q_(in) in order tomonitor the DL radio link quality of the PCell.

(3) The threshold value Q_(out) is defined as a level at which a DLradio link is not reliably received, i.e. a value corresponding to ablock error rate of 10% of PDCCH transmission considering a PCFICHincluding a transmission parameter.

(4) The threshold value Q_(in) is defined as a level at which DL radiolink quality is more significantly and reliably received than at Qout,i.e. a value corresponding to a block error rate of 2% of PDCCHtransmission considering a PCFICH including a transmission parameter.

4.3.2 Case of Method 1

As described in Method 1, the first cell may be independently configuredand activated with respect to the second cell. In this case, the firstcell may be an SCell and out-of-synchronization may be configured toconform to a PCell. That is, the UE monitors out-of-synchronization onlyin the PCell and regards all SCells as out-of-synchronization when thePCell is out-of-synchronization. In addition, the first cell activatedas the SCell may be deactivated according to an RRM result for thesecond cell.

4.3.3 Definition of Out-of-Synchronization in NCT

If a specific serving cell or CC does not transmit a legacy PDCCH sothat compatibility with a legacy system is not satisfied and a new typeof PDCCH (e.g. E-PDCCH) is transmitted, the following new determinationcriteria for out-of-synchronization is needed.

(1) Method I: Out-of-synchronization is determined by measuring DL radiolink quality using a CSI-RS and then mapping an error rate of a newPDCCH.

(2) Method II: Out-of-synchronization is determined by measuring a CRSor a CSI-RS of the second cell and then mapping an error rate of a newPDCCH.

(3) Method III: Out-of-synchronization is determined by measuring aDM-RS used to demodulate a new type of PDCCH and then mapping an errorrate of the new type of PDCCH.

The second cell, which is a non-synchronized cell, may securesynchronization by transmitting a signal (e.g. a PSS/SSS) necessary forsynchronization. The PSS/SSS may be transmitted in specific subframes(e.g. subframe indexes 0 and 5) of a radio frame.

An RS used to demodulate a PDSCH is categorized into a CRS and a UE-RSaccording to Transmission Mode (TM). In a legacy LTE Rel-10 system, anFDD UE-RS may overlap a PSS/SSS in a symbol position.

In this case, the UE-RS may be configured not to be transmitted on atime/frequency resource on which the PSS/SSS is transmitted so thatcollision between the PSS/SSS and DL data can be avoided. Notably, PDSCHdata is discarded on the time/frequency resource on which the PSS/SSS istransmitted.

Alternatively, the eNB may transmit the PDSCH data by resetting thelocation of the UE-RS in a subframe in which the PSS/SSS is transmitted.

FIG. 15 illustrates an example of a UE-RS pattern in a serving cell towhich a normal CP is applied in FDD.

Refer to FIG. 15, a horizontal grid illustrates UE-RSs for antenna ports7, 8, 11, and 13 and a vertical grid illustrates UE-RSs for antennaports 9, 10, 12, and 14.

The UE-RS pattern illustrated in FIG. 15 may be effectively configuredonly in subframes (e.g. subframes 0 and 5) in which a PSS/SSS istransmitted. More restrictedly, the UE-RS pattern may be effectivelyconfigured only in a frequency resource (e.g. 6 RBs) on which thePSS/SSS is transmitted.

If a CSI-RS is configured in a subframe in which the PSS/SSS istransmitted, the CSI-RS may be configured not to be transmitted when theCSI-RS is allocated to overlap the UE-RS defined in FIG. 15 on an RE.

As another method, a subframe in which the CSI-RS is transmitted may beconfigured not to overlap a subframe in which the PSS/SSS is transmittedso that collision between RE positions of the CSI-RS and the UE-RS canbe avoided.

5. Apparatus

Apparatuses illustrated in FIG. 16 are means that can implement themethods described before with reference to FIGS. 1 to 15.

A UE may act as a transmitter on a UL and as a receiver on a DL. An eNBmay act as a receiver on a UL and as a transmitter on a DL.

That is, each of the UE and the eNB may include a Transmission (Tx)module 1640 or 1650 and a Reception (Rx) module 1660 or 1670, forcontrolling transmission and reception of information, data, and/ormessages, and an antenna 1600 or 1610 for transmitting and receivinginformation, data, and/or messages.

Each of the UE and the eNB may further include a processor 1620 or 1630for implementing the afore-described embodiments of the presentdisclosure and a memory 1680 or 1690 for temporarily or permanentlystoring operations of the processor 1620 or 1630.

The embodiments of the present invention may be performed using thecomponents and functions of the above-described UE and eNB. For example,the processor of the UE may perform RRM for the first cell using aCRS/CSI-RS of the second cell when a CSI-RS of the first cell and theCRS and/or CSI-RS of the second cell are QCL and report a measurementresult to the eNB. In addition, the processor of the eNB may manage twoor more serving cells and transmit QCL information between cells to theUE, so that the UE may perform a QCL related operation. For details,refers to the contents described in sections 1 to 4.

The Tx and Rx modules of the UE and the eNB may perform a packetmodulation/demodulation function for data transmission, a high-speedpacket channel coding function, OFDMA packet scheduling, TDD packetscheduling, and/or channelization. Each of the UE and the eNB of FIG. 16may further include a low-power Radio Frequency (RF)/IntermediateFrequency (IF) module.

Meanwhile, the UE may be any of a Personal Digital Assistant (PDA), acellular phone, a Personal Communication Service (PCS) phone, a GlobalSystem for Mobile (GSM) phone, a Wideband Code Division Multiple Access(WCDMA) phone, a Mobile Broadband System (MBS) phone, a hand-held PC, alaptop PC, a smart phone, a Multi Mode-Multi Band (MM-MB) terminal, etc.

The smart phone is a terminal taking the advantages of both a mobilephone and a PDA. It incorporates the functions of a PDA, that is,scheduling and data communications such as fax transmission andreception and Internet connection into a mobile phone. The MB-MMterminal refers to a terminal which has a multi-modem chip built thereinand which can operate in any of a mobile Internet system and othermobile communication systems (e.g. CDMA 2000, WCDMA, etc.).

Embodiments of the present disclosure may be achieved by various means,for example, hardware, firmware, software, or a combination thereof.

In a hardware configuration, the methods according to exemplaryembodiments of the present disclosure may be achieved by one or moreApplication Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In a firmware or software configuration, the methods according to theembodiments of the present disclosure may be implemented in the form ofa module, a procedure, a function, etc. performing the above-describedfunctions or operations. A software code may be stored in the memory1680 or 1690 and executed by the processor 1620 or 1630. The memory islocated at the interior or exterior of the processor and may transmitand receive data to and from the processor via various known means.

Those skilled in the art will appreciate that the present disclosure maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent disclosure. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein. It is obvious to those skilled in the art thatclaims that are not explicitly cited in each other in the appendedclaims may be presented in combination as an embodiment of the presentdisclosure or included as a new claim by a subsequent amendment afterthe application is filed.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to various wireless access systemsincluding a 3GPP system, a 3GPP2 system, and/or an IEEE 802.xx system.Besides these wireless access systems, the embodiments of the presentdisclosure are applicable to all technical fields in which the wirelessaccess systems find their applications.

1. A method for performing Radio Resource Measurement (RRM) by a UserEquipment (UE) in a radio access system, the method comprising:receiving a higher layer signal including information about QuasiCo-Location (QCL) between a Channel State Information Reference Signal(CSI-RS) of a first cell and a Cell-specific Reference Signal (CRS)and/or a CSI-RS of a second cell; receiving the CRS and/or the CSI-RS ofthe second cell based on the information about QCL; and performing firstRRM for the first cell using the CRS and/or the CSI-RS of the secondcell.
 2. The method according to claim 1, wherein synchronization forthe first cell is maintained using a synchronization signal transmittedin the second cell.
 3. The method according to claim 1, furthercomprising performing second RRM for the first cell using the CSI-RS ofthe first cell.
 4. The method according to claim 3, wherein the firstRRM includes one or more of Reference Signal Received Power (RSRP)measurement and Path Loss (PL) measurement, and the second RRM includesone or more of Reference Signal Received Quality (RSRQ) and PLmeasurement.
 5. The method according to claim 1, wherein the first cellis a synchronized cell in which a synchronization signal is nottransmitted, the second cell is a synchronization reference cell inwhich the synchronization signal is transmitted, and the UE does notreceive a downlink signal from the first cell while the UE receives theCRS and/or the CSI-RS of the second cell from the second cell.
 6. Themethod according to claim 1, wherein the first cell is a New CarrierType (NCT) to which one or more of a synchronization signal, a CRS, adownlink broadcast channel, and a downlink control channel are notallocated, and the second cell is a legacy serving cell.
 7. The methodaccording to claim 1, wherein the UE selects any one of the CRS and theCSI-RS of the second cell indicated by the information about QCL anduses the selected one for RRM.
 8. A User Equipment (UE) for performingRadio Resource Measurement (RRM) in a radio access system, the UEcomprising: a transmission module; a reception module; and a processorsupporting the RRM, wherein the processor is configured to: receive ahigher layer signal including information about Quasi Co-Location (QCL)between a Channel State Information Reference Signal (CSI-RS) of a firstcell and a Cell-specific Reference Signal (CRS) and/or a CSI-RS of asecond cell through the reception module; receive the CRS and/or theCSI-RS of the second cell based on the information about QCL through thereception module; and perform first RRM for the first cell using the CRSand/or the CSI-RS of the second cell.
 9. The UE according to claim 8,wherein synchronization for the first cell is maintained using asynchronization signal transmitted in the second cell.
 10. The UEaccording to claim 8, wherein the processor is configured to furtherperform second RRM for the first cell using the CSI-RS of the firstcell.
 11. The UE according to claim 10, wherein the first RRM includesone or more of Reference Signal Received Power (RSRP) measurement andPath Loss (PL) measurement, and the second RRM includes one or more ofReference Signal Received Quality (RSRQ) and PL measurement.
 12. The UEaccording to claim 8, wherein the first cell is a synchronized cell inwhich a synchronization signal is not transmitted, the second cell is asynchronization reference cell in which the synchronization signal istransmitted, and the UE does not receive a downlink signal from thefirst cell while the UE receives the CRS and/or the CSI-RS of the secondcell from the second cell.
 13. The UE according to claim 8, wherein thefirst cell is a New Carrier Type (NCT) to which one or more of asynchronization signal, a CRS, a downlink broadcast channel, and adownlink control channel are not allocated, and the second cell is alegacy serving cell.
 14. The UE according to claim 1, wherein the UEselects any one of the CRS and the CSI-RS of the second cell indicatedby the information about QCL and uses the selected one for RRM.